1. Field of the Invention
The present invention relates to a method and apparatus for producing a crosslinked foamed article. During the process when the article is produced, the resin extrudate can progress through the mold smoothly.
2. Description of the Prior Art
Crosslinked foamed articles have the advantage of light weight and have been frequently used as insulating material, shoe material, cushion material, and in sporting goods. The raw materials for producing crosslinked foamed articles include thermoplastics (e.g., PE, PP, and EVA) and thermoset resins (such as rubbers). Nowadays, the production of crosslinked foamed articles can be classified into the following two methods:
(1) The polymer composition is mixed, extruded or molded to a sheet, and finally molded under pressure batchwise into a crosslinked foamed article: PA1 (2) The polymer composition is mixed, extruded or molded to a foamed sheet, and finally subjected to batchwise crosslinking into a crosslinked foamed article. PA1 (a) uniformly mixing at least one crosslinkable resin, at least one crosslinking agent, at least one foaming agent, and some additives into a resin composition; PA1 (b) extruding the resin composition through a die into an extrudate of a predetermined shape; and PA1 (c) heating the extrudate to a temperature sufficient to cause crosslinking and foaming of the crosslinkable resin while being driven by a driving device to move in the extruding direction, thereby obtaining a crosslinked foamed article. PA1 an extruder for heating a crosslinkable resin composition into a molten resin composition, the resin composition containing at least one crosslinkable resin, at least one crosslinking agent, and at least one foaming agent; PA1 a die, connected to the extruder, from which the molten resin composition can be extruded into a extrudate of a predetermined shape; PA1 a heating mold for receiving and heating the extrudate to a temperature sufficient to cause crosslinking and foaming of the crosslinkable resin; and PA1 a driving means for driving the extrudate in the heating mold to move in the extruding direction.
However, the above two methods are employed in batches, thus increasing energy and production cost. Therefore, a continuous process of simultaneous crosslinking and foaming has been developed.
For example, Kimura et al. in U.S. Pat. No. 4,552,708 uses a long-land die to maintain the pressure in order to obtain a foamed article of good properties. However, in order to make the plastic materials progress smoothly through the mold, lubricant should be continuously applied to decrease friction.
Yamamoto et al. in U.S. Pat. No. 5,310,513 uses a two-zone long die. In the front zone, the plastic material is heated to cause crosslinking. In the rear zone, the crosslinked product is cooled. Finally, the crosslinked product is heated to freely expand and foam to obtain a final crosslinked foamed article. Thus, the final cross-linked foamed article having nonuniform and large bubbles is generated due to free foaming.